Must buy those Sol Stein books...
I think of a 'scene' as a unit of change - change being the chief motor of narrative drive - and the book as being built up of a series of those units. Usually in my work it'll be an encounter between two people, but it might be just the MC doing something on their own, or an external event which the characters are involved in. But either way, all the actions and interactions (considering speech as an action) build up to that moment of change, when something significant about the character's situation/thought/nature/knowledge shifts. The rest of the scene is about the result of that shift (do they realise? do others? what happens because of it?) and also covertly setting up the next scene/change, so it's convincing when the narrative starts to build up to that.
Of course there are things in between these big moments, but one of the most common things wrong with manuscripts I do reports on is that there's too much in between which moves the characters around their ordinary lives but doesn't actually contribute to climb up to a change or the run down from it, and therefore doesn't actually do anything to help the narrative drive. The Narrative structure thread here:
http://www.writewords.org.uk/forum/65_250192.asp
gets talking about jump-cuts versus taking the reader with you, which might illuminate this a bit.
Emma